Security researchers exploited previously unknown vulnerabilities in Apple Safari, Google Chrome and Flash Player to compromise the latest versions of OS X and Windows during the first day of the annual Pwn2Own hacking contest.

On Wednesday, four teams and a researcher who competed on his own made six attempts to hack this year's targets: Safari running on OS X, Chrome running on Windows, Microsoft Edge running on Windows and Flash Player on Windows. Four attempts were successful, one was only partially successful and one failed.

The 360Vulcan Team from Chinese Internet security company Qihoo 360 combined a remote code execution vulnerability in Flash Player with a vulnerability in the Windows kernel to gain system privileges. For this feat, they received a US$80,000 prize, $60,000 for the Flash Player exploit and a $20,000 bonus for the system-level escalation.

Later in the day, the same team demonstrated a remote code execution attack against Google Chrome on Windows that members also managed to escalate to system. For that attack, they combined exploits for four vulnerabilities: one in Chrome, two in Flash and one in the Windows kernel.

The attack was considered only a partial win, because the Chrome flaw had previously been reported to Google by an independent researcher without the team's knowledge, so it didn't qualify as a zero-day. The team still won $52,500, putting their first-day payout at $132,500.

South Korean researcher JungHoon Lee, known in hacking circles as lokihardt, demonstrated a remote code execution attack against Apple Safari on OS X with an escalation to root privileges. He also combined four vulnerabilities, earning a $60,000 prize.

This year, Safari exploits are rewarded with $40,000, compared to $60,000 for Chrome and Microsoft Edge on Windows. The privilege escalation bonus of $20,000 is available for both Windows and OS X.

It's worth noting that during last year's edition of Pwn2Own, JungHoon Lee was the most successful contestant, taking home $225,000, almost half of the total payout.

He still has time to come on top this year, too, because he was scheduled to attempt attacks against Chrome and Microsoft Edge on Thursday, the contest's second day. Meanwhile, 360Vulcan Team, which is currently in the lead, has no other demonstrations scheduled.

Chinese Internet giant Tencent has three teams in the contest, with members from several of its subsidiaries.

During the first day, Tencent Security Team Shield demonstrated an attack against Safari to achieve root-level code execution. The exploit combined two vulnerabilities, one in Safari and one in another privileged process, and earned the team $40,000.

Meanwhile, Tencent Security Team Sniper demonstrated an attack against Flash Player on Windows that involved privilege escalation to system, for which the group received $50,000.

The third Tencent team, Xuanwu Lab, tried an exploit against Adobe Flash in Microsoft Edge, but it failed to work.

During the first day, security researchers won $282,500 and disclosed 15 previously unknown vulnerabilities. The exploits were shared with contest organizers from the Zero Day Initiative, which is now part of Trend Micro, and will be reported to the affected vendors.

This year, the Pwn2Own contest is sponsored by Trend Micro and Hewlett Packard Enterprise and has a total prize pool around $600,000.